bones moving around and misbehaving
The reason why you are having issues is because your spine isn't a single unified chain. Normally, the spine bones start at the hips and move up the back and ends in the head. Legs and arms can then be placed relative to those bones.
Add in a bone on the ground below the neck and extend it up so it ends in between the spine and head. This will be your root bone. Parent the spine bone, the arm bones, and the neck bone to the root bone. Be sure to uncheck the deform option in the bone tab on the root bone.